Reaction Kinetics, Mechanisms and Catalysis最新文献

The current study describes synthesis of CdO Ag-doped CdO nanoparticles via a simple co-precipitation route and characterization of nanoparticles by SEM, XRD, EDX and FTIR techniques. The photocatalytic performance of CdO and Ag-doped CdO nanoparticles were evaluated by degradation of difenoconazole pesticide in the presence of sunlight considering the effect of pH, catalyst dosage, contact time, initial difenoconazole concentration and temperature. The degradation efficiencies of CdO and Ag-doped CdO were proficient at pH 4 and 6. The photodegradation abilities of CdO and Ag-doped CdO enhanced with catalytic dosage up to 0.06 g and 0.05 g with 42% and 54% removal of difenoconazole. The degradation capabilities of CdO and Ag-doped CdO increased with contact time by 43% and 65% removal of difenoconazole. The degradation of difenoconazole by CdO and Ag-doped CdO enhanced with initial pesticide concentration up to certain level but declined after the threshold value. The rate of degradation of difenoconazole by CdO decreased with temperature but enhanced by Ag-doped CdO with increase in temperature up to 50 °C and then declined with further temperature. This research emphasizes that doping of Ag in microstructure is an innovative strategy to enhance the photocatalytic efficiency of CdO nanoparticles.

In this work, Keggin heteropolyacid cesium salts were evaluated as solid catalysts in reactions to obtain terpene acetals, which are attractive products to the pharmaceutical and fine chemical industries. Salts of cesium (Cs₃PW₁₂O₄₀, Cs₃PMo₁₂O₄₀, and Cs₄SiW₁₂O₄₀) were obtained through precipitation of Keggin heteropolyacids with Cs₂CO₃ and used in reactions of condensation of β-citronellal with alkyl alcohols (methyl, ethyl, propyl, butyl, and isopropyl) at room temperature. Among the salts tested, the Cs_2.5H_0.5PW₁₂O₄₀ was the most active and selective catalyst toward the β-citronellyl methyl acetal. The superior performance of cesium phosphotungstate salt was assigned to the increase in acidity strength of protons remaining in the phosphotungstate anion, whereas the observed difference in the two other cesium heteropoly salts. The effects of temperature, time, alcohol nature, and catalyst load were evaluated. The use of solid, easily synthesizable, and non-corrosive catalysts in acetalization reactions at room temperature comprises a positive aspect of this process.

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This study successfully explains the kinetic and thermodynamic behavior of oxidative coupling reactions between 4-amino-N,N-dimethylaniline and various para-substituted phenol derivatives using potassium dichromate in alkaline medium. All reactions were confirmed to follow first-order kinetics. The comprehensive determination of activation parameters (E_a, k, ΔH*, ΔS*, and ΔG*) for each derivative, revealing clear trends based on electronic effects. Electron-withdrawing groups (F, Cl, Br, I) significantly reduced activation energies, with 4-bromophenol exhibiting the lowest E_a (11.02 kJ/mol), while electron-donating substituents raised the activation energy, with 4-methoxyphenol showing the highest (29.32 kJ/mol). Notably, 4-iodophenol presented an exceptional combination of low ΔH* (8.357 kJ/mol) and highly negative ΔG* (− 65.07 kJ/mol), attributed to favorable entropy contributions, indicating strong spontaneity. Complementary DFT calculations using the 6-311G(d,p) basis set confirmed these results, showing consistent trends with experimental data, while highlighting differences in energetic magnitudes. Theoretical analysis confirmed the influence of substituent electronics on reactivity and intermediate stability.

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A COMSOL Multiphysics-based model was developed to simulate medical transfusion tubing (MTT) pyrolysis using a "two-step five-reaction" kinetic scheme. This approach systematically elucidates how critical parameters, such as the heating rate (5–50 °C/min), pyrolysis temperature (400–500 °C), and reaction heat, govern the product yield and heat/mass transfer dynamics. The results demonstrated a strong dependence of the reaction rate on the pyrolysis temperature. Complete MTT conversion was achieved at 500 °C within 9.2 min, whereas lower temperatures (400–425 °C) retained 11.9% and 1.8% of intermediate solids after 60 min. Furthermore, the reaction rate was governed by both the heat supply and reactant concentration, highlighting the intricate coupling between thermal and chemical dynamics. Parallel/tandem reaction pathways were resolved for volatile and solid products, and the heating rate increased (5–50 °C/min), elevating the volatile₂ yield (15.4–17.5%) and reducing the volatile₁ (33.6–32.1%) and solid₂ (11.1–10.4%) yields. An increase in pyrolysis temperature (400–500 °C) increased the concentration of Volatile₂ (9.9–17.5%). Endothermic delays prolonged internal temperature equilibration by 79.7% (1.6–7.9 min).

This research focused on the photocatalytic conversion of glycerol, a by-product of biodiesel, to lactic acid under mild conditions. For this purpose, Al₂O₃/nanotube-TiO₂ catalysts were prepared, characterized and the obtained catalysts were evaluated to investigate various reaction parameters and determine the optimum reaction conditions. The effects of catalyst reduction, oxygen presence, catalyst loading and NaOH/glycerol molar ratio were investigated to evaluate the reaction conditions. The optimum result was obtained with a NaOH/glycerol molar ratio of 4 at 90 °C using 0.25 g of catalyst. This reaction, carried out with a 2.5% Al₂O₃/nt-TiO₂ catalyst, resulted in a lactic acid selectivity of 97.2% and a glycerol conversion of 60.1%.

In this article, the strip catalyst of NA(nano-alumina) and PB (pseudo-boehmite) were prepared as binders to explore the effect of the amount of binder on the performance of the strip catalyst. The performance of the forming catalyst was analyzed by XRD, SEM, NH₃-TPD and FTIR. The rare earth tailings-based strip catalysts prepared using Bayan Obo rare earth tailings as raw material with binder addition exhibit excellent denitration activity and mechanical strength. The catalyst prepared using NA as the binder demonstrates superior denitration performance compared to the catalyst formed with PB as the binder. In the range of 100 to 500 ℃, the selective catalytic reduction (SCR) efficiency of rare earth tailings is only 8.2%; the SCR efficiency of strip catalyst prepared with 15% NA gel is 62.5% and the longitudinal compressive strength is 1.15 MPa. After adding aluminum sol (NA or PB), the denitration performance of rare earth tailings increased by 54.3%. This study has certain guiding significance for the preparation of denitration catalyst of rare earth tailings.

The present work focuses on studying the adsorption process of methylene blue (MB) from aqueous solutions using activated Juglans regia shells. The methylene blue adsorption tests were analyzed in static mode (batch). Moreover, optimizing the parameters governing the MB adsorption process (m_ads, particle size, [MB], and time of contact) was performed using a Box-Behnken plan to minimize the time and number of experiments. The results showed that MB adsorption is almost complete, with a removal rate reaching 94.21%. The ANOVA analysis of variance showed that the postulated model is statistically adequate to describe the experimental results (R² = 99.54%) and (R²adj = 97.34%), and the residuals confirmed this perfect correlation between the experimental and theoretical data. Optimization by composite desirability (D = 1000) resulted in a maximum removal yield (R = 94.21%) for the optimal conditions. The modeling study suggests that the process of methylene blue uptake follows the pseudo-second order model with a maximum adsorbent quantity of 52.73 mg g⁻¹.

The mathematical modeling for aspirin crystallization via the gas antisolvent process was investigated. In addition, aspirin was precipitated experimentally from an ethanol solution using CO₂ as an antisolvent in the supercritical condition. Breakage, agglomeration, nucleation, and growth kinetics are essential for modeling the process and controlling the particle size later. The current study deployed equations of state, population balance, and material balance equations. Since such models are intricate, a robust numerical algorithm was adopted. Furthermore, the kinetic parameters were identified by applying the maximum likelihood method with the aid of the genetic algorithm using the experimental data. Comparison between the experimental and modeling data revealed that the model could closely predict the particle size distribution. The results indicated that increasing the antisolvent addition rate and the operating temperature would decrease the mean particle size. Moreover, a bimodal particle size distribution was obtained at a lower antisolvent addition rate and temperature.

MoO₃/Al₂O₃ solid acid catalysts with MoO₃ loadings of 20, 50, and 80 mol% were synthesized via the impregnation method and extensively characterized using XRD, TG–DTA, N₂ adsorption–desorption, IR spectroscopy of adsorbed pyridine, and potentiometric titration. Increasing MoO₃ loading induced a clear structural evolution from highly dispersed Mo species to crystalline MoO₃ and Al₂(MoO₄)₃ phases. Textural analyses revealed a progressive reduction in surface area and pore volume due to partial pore blockage by Mo-containing phases. Acidity measurements indicated a substantial increase in total acid site density and a distinct shift from Lewis-dominant to Brønsted-dominant acidity with higher MoO₃ content. Catalytic testing for isopropanol dehydration in the 260–400 °C range showed that the MA-80 catalyst achieved complete (100%) conversion to propene at all tested temperatures and exhibited zero apparent activation energy, indicating exceptional catalytic efficiency. Lower-loaded catalysts required higher reaction temperatures to reach full conversion and displayed reduced activity. The superior performance of MA-80 was attributed to the predominance of Brønsted acid sites and enhanced acid strength, underscoring the pivotal role of MoO₃ loading in tuning surface acidity and optimizing catalytic performance for alcohol dehydration processes.